Refining lead



Patented Dec. 14, 1937 PATENT OFFIC BEFINING LEAD Jesse 0. Betterton and Yurii E. Lebedefl, Metuchen, N. and Refining Company, poration of New Jersey J., assignors' to American Smelting New York, N. Y., a cor- No Drawing. Application September 26, 1936,

Serial No.

6 Claims. (01. 25-783 This invention relates to the art of removing bismuth from lead and provides certain improvements in that art by which marked economies are effected in producing lead of very low bismuth content.

It is well known that bismuth may be removed from lead by incorporating one or more alkaline .earth metal reagents in a bath of lead, allowing the bath to cool and separating the alkaline earth bismuthides from the bath. Such a process, employing calcium and magnesium as the alkaline earth metal reagents, is set forth in United States Letters Patent No. 1,853,540, granted April 12, 1932, to Jesse O. Betterton.

Although it is possible to eliminate substantially all the bismuth from lead in accordance with the process of that patent, the bismuth content is lowered to only about 0.02% in commercial practise as the relatively large quantity of reagent required to lower the bismuth content materially below that figure would greatly in-' crease the cost of the operation. Accordingly, a typical analysis of the lead refined commercially with calcium and magnesium will show approximately 0.02% bismuth and approximately 0.045% each of calcium and magnesium. f

It is also known, as disclosed in United States Letters Patent No. 2,056,164, granted October 6, 1936, to Jesse O. Betterton and Yurii E. Lebedetf, that antimony and arsenic are effective debismuthizing agents under certain conditions as shown by the fact that they will further lower the bismuth content of lead previously debismuthized with alkaline earth metals. In other words, after the debismuthizing action of alkaline earth metal reagents is complete, the bismuth'content of the lead may be further lowered by the proper use of antimony and/or arsenic, either in elemental or alloy form.

The present invention is directed to the use of antimony as a debismuthizing reagent in refining lead and constitutes an improvement of the invention covered by United States Letters Patent No. 2,056,164.

It has been found in debismuthizing lead with antimony that the debismuthizing action is effected by the formation and separation of a compound or product of definite, fixed composition (antimony-bismuth-calcium-magnesium) a n d that a critical ratio of antimony to bismuth exists which favors the maximum formation of this compound or product and is, therefore, a factor of major importance in determining the emciency of the debismuthizing action of the antimony. Further, it has been found that the maximum formation of the compound or product of fixed composition is also enhanced by slowly incorporating the antimony in the lead bath, at minimum temperatures.

Based on these discoveries, the invention is 5 practiced for the most economical and efiicient' bismuth removal, by adjusting the antimony addition to approximately six times the bismuth content of the lead treated and incorporating it in the lead at a minimum working temperature 10 (approximately 630 F. to approximately 640* F.). The antimony is preferably worked into the bath a portion at a time rather than as a single addition. The calcium and magnesium contents when the antimony is added to the bath should each be 15' about one and a quarter to one and a half times the bismuth content.

The efficiency of the invention, various manners in which it may be practiced and the advantages to be derived from its use are well illustrated by the specific examples and tabulated results hereinafter set forth.

It will be observed from an examination of Table I in which are set forth the results from five runs that were identical except for the quantity of antimony used, that the lowest bismuth final (0.003% Bi) was obtained in run No. 3 in which the antimony addition was six times the bismuth content. Further, the final metal in this run contained only 0.001% antimony.

In each of the five runs, equal amounts of lead which hadbeen previously debismuthized with calcium and magnesium were used, the lead being charged to an ordinary kettle and the oxide dross formed during the melting down period removed. 5 The respective baths, before addition of the antimony, analyzed 0.025% Bi, 0.043% Ca and 0.041% Mg.

An antimony-lead alloy containing 12.1% Sb was utilized as the source of antimony (antimony alone may be used as well) and the requisite amount of alloy cut into ten pieces. Each piece of the alloy wasadded to the bath at 630 F. via the vortex created by a mixer, the charge stirred until the alloy was incorporated in the bath, and the bath settled for an equal period of time without agitation. following which another piece of alloy was added. When all the antimony had been added in this manner the bath was settled at 640 F.-650 F. without agitation for one hour,

then cooled to freezing and the refined metal withdrawn from under the frozen crust. The final metal analyses for the various antimony additions are given in Table I.

Attention is directed to the fact that the lead ,66

used in these runs represents a typical analysis of lead as commercially refined by calcium and magnesium and that excessive quantities of these reagents would be required to materially lower its bismuth content. Further, it is evident that the antimony is the debismuthizing reagent by reason of its ability to remove the bismuth from the lead by forming the quaternary compound or product of fixed composition in the presence of the residual but ineiiectual alkaline earth metal reagents.

TableI Analysis ofiinal Sb addimetal Run No. tion,

. lbs./ton Bi Ca Mg 1.37 0.014 0.031 0.020 2.54 0.007 0.010 0.014 3.00 0.003 0.012 0.010 5.62 0.012 None None 7.47 0.016 None None The beneficial effect to be obtained by incorporating the antimony inthe bath at the minimum working temperature not exceeding approximately 640 F. is shown by results of the comparative runs which are shown in Table II. In each case the lead used contained 0.03% Bi, 0.07% Ga and 0.034% Mg and the antimony additions were identical. The only variation in procedure of the various runs was that of the temperature at which the antimony additions were made. The results clearly show thatthe antimony exerts its maximum debismuthiz'ing action at temperatures approaching the freeezing point of the bath.

It has already been mentioned that it is advantageous to add the antimony or antimony al- 10y to the bath slowly, i. e., a portion at a time as contrasted to adding the whole amount at one time. This is illustrated by the results of runs 11 and 12 set forth in Table .111.

' In run 11, the requisite antimony in the form of a 12.1% Sb lead-antimony alloy was added to the molten bath at 630 F. in a single addition. In run 12 the antimony was supplied in the same form (12.1% Sb lead-antimony alloy) but cut into ten peces and incorporated in the bath at 630 F. a piece at a time. In each case the bath was settled for an hour without agitation at 640 F. to 650 F. and the metal withdrawn from under the frozen crust.

'It is believed that the results of the various runs herein set forth clearly demonstrate that maximum removal of bismuth by antimony is a corollary of maximum formation of the quaternary compound or product already mentioned. The fixed composition of the compound or product is shown by Table IV in which the analyses of the compounds or products of the respective drosses separated in runs 1, 2, and 3 (Table I) are set forth.

Table IV Run Percent Percent Percent Percent Sb B1 Ca Mg 63. 5 ll. 2 11. 2 l4. 1 64.8 9.3 12.4 13.5 64.4 9.4 13.2 12.9

of antimony is as much to be avoided as an insufliciency of that reagent. Further, it is apparent from theresults set forth in Table II that at low temperatures antimony exhibits its maximum efficiency in forming the desired quaternary compound and is much less capable of replacing bismuth in alkaline earth metal combinations than it is at high temperatures.

The invention may be applied with equal success either to lead containing residual alkaline earth metals by reason of previous treatment with such reagents for the removal of bismuth or to lead containing no alkaline earth metals. In the former case, the compound or product of fixed composition can usually be formed simply by adding the requisite amount of antimony at the proper low temperature as hereinbefore described. In the latter case, which will ordinarily be encountered in operations where the bismuth content is objectionable but less than about 0.015 to 0.02 per cent, and, accordingly, would require excessive quantities of alkaline earth metals if the lead were to be debismuthized with those reagents, suitable small alkaline earth metal additions are easily made prior to the requisite antimony addition. In all other respects, the treatment of the two kinds of starting material is the same. I

It will thus be appreciated that the present invention provides definite advantages and improvements in debismuthizing processes utilizing antimony as the debismuthizing reagent. It will also ,be appreciated that while the invention has been explained and illustrated by various specific disclosures, both as regards methods of operation and analyses or compositions of materials, it is not necessarily limited thereby and that, accordingly, the invention is to be deemed to embrace such changes and modifications employing its principle as will become apparent to those skilled in the art.

What is claimed is:

1. The process for debismuthizing lead containing alkaline earth metals in amounts insuiiicient'to effect any substantial reduction of the bismuth content of the lead but suflicient to permit the formation of a fixed compound or product of antimony, bismuth and alkaline earth metals which comprises slowly incorporating an amount of antimony equal to approximately six times the bismuth content of the lead into a bath of the lead within a minimum working temperature range, cooling the bath to freezing and separating the liquid metal and frozen crust thereby eflecting substantially complete removal of bismuth from the lead.

2. The process for refining lead "containing bismuth and from about 1.25 to 1.5 times the bismuth content of each of calcium and magnesium which comprises incorporating antimony in a bath of such lead in amount calculated to remove all of the bismuth as a quaternary composition of antimony, bismuth, calcium and magnesium,-the addition of antimony being accomplished slowly in multiple additions at the mini mum working temperature of the bath.

3. In refining lead containing bismuth and alkaline earth metals with antimony, the improvement which consists in adding the antimony to a. bath of such lead at a. temperature not exceeding approximately 640 F. and in amount closely approximating'six times the bismuth content of the bath.

4..In refining a bath of lead. containing bismuth and alkaline earth metals with antimony,

the improvement which consists in adding the antimony to the bath in portions and settling the bath between such additions.

5. In refining lead containing bismuth and alkaline earth metals with antimony, the improvement which comprises incorporating in the lead an amount of antimony equal to approximately six times the bismuth content of the lead.

6. The process for debismuthizing lead with calcium, magnesium and antimony which comprises adjusting the calcium and magnesium contents of a bath of the lead each to about one and one-fourth to one and one-half times the bismuth content of the bath, incorporating antimony in the bath at a relatively low temperature and in amount approximating six times the bismuth content, and efiecting a separation between the resulting dross and the debismuthized lead.

JESSE O. BE'I'I'ERTON. YURII E. LEBEDEFF. 

